Based on the commitments offered by the companies, British regulators have withdrawn their request to the Commission to review the planned merger, which can now go ahead.
The companies must now sell a quarter of the combined spectrum of the merging firms in the 1800 MHz band, which rivals could use to offer faster mobile broadband.
Together, T-Mobile and Orange will have a UK market share of about 37% putting them ahead of current British market leaders O2 and Vodafone.
Orange is the number three brand in the domestic market, followed by T-Mobile.
In a statement, the European Commission says: “The (approval) decision is conditional upon the amendment of an existing network sharing agreement with Hutchison 3G UK (3), to ensure that there remain sufficient competitors in the market.”
The two companies plan to keep the T-Mobile and Orange brands for the first 18 months and then review the strategy.